1. Field of the Invention
The present invention relates to an imaging device and an imaging method that are suitable for application to e.g. an imaging device that can carry out variable speed ramping.
2. Description of the Related Art
In an imaging device employing a frame-transfer (FT) charge coupled devices (CCD) image sensor, the image area (light receiving part) is shielded from light during signal charge readout. Furthermore, in an imaging device employing a complementary metal oxide semiconductor (CMOS) image sensor, the image area is shielded from light during charge readout in order to achieve simultaneity of signal charge accumulation.
A scheme of using a rotary shutter is known as a method for shielding the image area from light. In general, the rotation of the rotary shutter is controlled in synchronization with the drive timing of the imaging element.
FIG. 5 shows the relationship between the operation of a rotary shutter and the drive timings of an imaging element in an FT-CCD. The FT-CCD includes an imager part (imaging area), a storage part (accumulation area), a horizontal transfer register, and a charge detector. FIG. 5 shows the correspondence between the operation in the imager part and the storage part and the operation of the mechanical shutter formed of the rotary shutter.
The uppermost row of FIG. 5 shows the output timings of a vertical reset signal for giving an instruction to transfer a charge from the imager part to the storage part. The next row shows the open/close operation of the mechanical shutter formed of the rotary shutter. The remaining rows show the operation in the imager part and the operation in the storage part. As the operation of FIG. 5, the operation in an imaging device that carries out variable speed control of the electronic shutter is taken as an example.
First, an all-pixel sweep-out signal for giving an instruction to sweep out all of the accumulated charge is input to the imager part. Thereupon, all of the charge that has been accumulated in the imager part until this timing is swept out. Thereafter, a charge is accumulated in the imager part until the vertical reset signal is input. This accumulation time serves as a so-called exposure time. Upon the input of the vertical reset signal, the charge is read out from the imager part and transferred to the storage part at high speed.
Simultaneously, in response to the input of the vertical reset signal, the rotational phase of the mechanical shutter is so controlled that a light-blocking part of the rotary shutter is disposed in front of the imaging element. Due to this operation, the image area is shielded from light during the period of the charge transfer from the imager part to the storage part.
For example, Japanese Patent Laid-open No. 2006-308841 discloses a shutter device that controls the period of the incidence of light to the imaging plane of a solid-state imaging element and the period of blocking of light to the imaging plane.